Waveguide transition piece with low reflection

ABSTRACT

A waveguide transition piece for the broadbanded, low reflection connection of standard rectangular waveguides with smooth or corrugated waveguides with an oval inner cross section. The transition piece is a waveguide with a rectangular inner cross section, and with the central portion of the longer sides of the inner cross section having a widened portion which extends, in the form of linearly widened conical sections over a length of no more than 0.85 waveguide wavelengths in the direction toward the end of the transition piece to which the oval waveguide is to be connected, the widened portion serving substantially to effect a broadbanded matching of the characteristic impedance of the two adjacent waveguides having different inner cross sections which are to be connected by means of concentrated adapter elements which act, at the point where they are disposed, predominantly as parallel capacitances or parallel inductances. The transition piece includes a further waveguide section which is disposed between the connecting plane with the oval waveguide and the end of the waveguide section having the conically widened portion.

United States Patent Kaffenberger et al.

[ Dec. 23, 1975 [75] Inventors: Ernst Kaffenberger; Erich Schiittliiffel, both of Backnang, Germany [73] Assignee: Licentia Patent-Verwaltungs-G.m.b.H., Frankfurt am Main, Germany [22] Filed: May 3, 1974 [21] Appl. No.: 466,861

30 Foreign Application Priority Data May 4, 1973 Germany 2322429 May 4, 1973 Germany 7316744 [52] US. Cl 333/34; 333/21 R; 333/98 R [51] Int. Cl. H01? l/16; HOlP 5/08 [58] Field of Search 333/32, 33, 34, 35, 21 R, 333/21 A, 98 R, 27

[56] References Cited UNITED STATES PATENTS 3,336,543 8/1967 Johnson et a1. 333/21 R X 3,388,352 6/1968 Ramonat 333/98 3,686,589 8/1972 Spinner et al 1 333/21 R 3,686,595 8/1972 Spinner l .1 333/98 R 3,818,383 6/1974 Willis 333/21 R Primary ExaminerJames W.. Lawrence Assistant Examiner-Marvin Nussbaum Attorney, Agent, or FirmSpencer & Kaye [57] ABSTRACT A waveguide transition piece for the broadbanded, low reflection connection of standard rectangular waveguides with smooth or corrugated waveguides with an oval inner cross section. The transition piece is a waveguide with a rectangular inner cross section, and with the central portion of the longer sides of the inner cross section having a widened portion which extends, in the form of linearly widened conical sections over a length of no more than 0.85 waveguide wavelengths in the direction toward the end of the transition piece to which the oval waveguide is to be connected, the widened portion serving substantially to effect a broadbanded matching of the characteristic impedance of the two adjacent waveguides having different inner cross sections which are to be connected by means of concentrated adapter elements which act, at the point where they are disposed, predominantly as parallel capacitances or parallel inductances. The transition piece includes a further waveguide section which is disposed between the connecting plane with the oval waveguide and the end of the waveguide section having the conically widened portion.

US, Pawn Dec. 23, 1975 3,928,825

WAVEGUIDE TRANSITION PIECE WITH LOW REFLECTION BACKGROUND OF THE INVENTION The present invention relates to an improved waveguide transition piece for the broadbanded low reflection connection of standard rectangular waveguides with smooth or corrugated waveguides having oval cross sections. More particularly, the present invention relates to such a waveguide transition piecewherein the interior of this transition piece is in the form of a waveguide with a preferably standard rectangular cross section becomes wider in the center of its long sides, this widened section extending in the form of linearly widening conical sections over an area of no more than 0.85 waveguide wavelengths in the direction toward the junction with the oval waveguide and serving substantially to permit an effective broadbanded characteristic impedance matching of the two adjacent waveguides with different internal cross sections by means of concentrated adapter elements which act predominantly as parallel capacitances or parallel inductances at their point of attachment.

In order to connect oval waveguides (which are often used as semiflexible, smooth or corrugated connecting lines between spatially separated parts used in the superhigh frequency range) with standard rectangular waveguides (which serve in almost all of these systems as the output or input line sections), waveguide transition pieces are required which permit low reflection connection of these two types of waveguides. It is known for this purpose to continually widen the inner cross section of rectangular waveguides in the form of conical sections in the center of the long cross-sectional sides and in the direction toward the oval waveguide over a section of about three fourths of a waveguide wavelength. The reason for this widening of the cross section is to influence only the input resistance in the connecting plane between the waveguide transition and the oval waveguide so that concentrated elements which act predominantly capacitively or inductively at their point of attachment in the transition piece permit good matching of the characteristic impedance over sufficiently wide frequency bands. In the above-mentioned known embodiment, the concentrated adapter elements usually employed are capacitively acting screw-in plugs which permit subsequent compensation of overly wide manufacturing tolerances. Since the matching of such screw-in plugs in a test field and the sealing of such plugs involves high labor costs, preference has recently been given to the use of soldered-in fixed plugs, rather than the screw-in plugs, with a simultaneous reduction in the manufacturing tolerances. The alignment and soldering of the plugs, however, also requires additional working steps and relatively high labor costs.

SUMMARY OF THE INVENTION It is therefore the object of the present invention to avoid the drawbacks resulting from the above-mentioned methods.

This is accomplished according to the invention in that in a waveguide transistion piece having a rectangular inner cross section with the central portion of the longer sides of the rectangular cross section being continuously widened, in the form of conical sections over a length of no more than 0.85 waveguide wavelengths and in the direction toward the waveguide with the oval cross section, one or a plurality of further waveguide sections of a length of no more than A are provided between the end of the conical waveguide widening and the connection plane to the oval waveguide, so that conical widening of the waveguide transition piece ends a certain distance before the connecting plane with the oval waveguide. If these further sections are formed with rectangular inner cross sections which are widened by circularly cylindrical portions in the cen ters of their longer sides, these further sections, which constitute concentrated adapter elements and which act predominantly capacitively or inductively, will produce good matching of the waveguides with the standard rectangular cross section and the waveguide with the oval cross section which are to be connected by means of the waveguide transistion piece. The diameter of the circularly cylindrically widened waveguide'portions may be equal to the greatest diameter of the conically widened portion or it may be different therefrom depending on respective characteristic impedance conditions. I

For waveguide transition pieces which are to produce 'an extremely good matching of the different type waveguides to be connected over relatively broad frequency bands, it may be necessary to employ additional concentrated adapter elements. These can also be produced by waveguide sections whose rectangular cross section is widened in the center of the longer sides by cylindrical sections whose length is no more than )t In those cases where, in order to perform their respective electrical functions, these widened portions are most favorably applied or inserted in that section of the transition piece which is widened by conical portions, the linear path of the widened cross section is interrupted at their point of insertion and is replaced by a cylindrically widened portion whose diameter is different from those of the adjacent conically widened portions. 1

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1a is a longitudinal sectional view of one embodiment of a transition piece according to the inventron.

FIG. 1b is a cross-sectional view along the line A-A of FIG. la.

FIG. 2 is a plot of the loci of the input admittance of the waveguide transition piece in the connection plane with the oval waveguides for different configurations.

FIG. 3 is a longitudinal sectional view of a modified transition piece according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS. 12 and lb, there is shown one embodiment of a transition piece according to the invention which in general comprises a piece of waveguide with a rectangular inner cross section having longer sides X and shorter sides Y. The piece of waveguide includes a section 1 at the end thereof to which a standard rectangular waveguide is to be connected which also has the rectangular inner cross section. This section 1 is followed by a further section 2 which likewise has the same rectangular inner cross section. However, in the section 2 of the transition piece, the central portions of the longer sides X of the rectangular inner cross section is linearly widened, in the direction toward the end of the transition piece to which the oval waveguide is connected, by means of conical portions 6. As illustrated the length of the section 2 containing the conically widened portion should be less than 0.85 of a waveguide wavelength (A in the operating frequency band.

According to the preferred embodiment of the invention, the section 2 also includes a section 3 which interrupts the conical portion 6 and whose rectangular inner cross section is widened in the central portions of its longer sides X by circularly cylindrical section 7. The diameter of cylindrical section 7 is, in the illustrated embodiment, smaller than the diameter of the conical portion 6 at the location of section 3. It is to be understood however that the diameter of section 7 may be larger than the diameter of the adjacent portions of conical portion 6 and may be, if desired equal to the largest diameter of the conical portion 6. As illustrated the length of the cylindrical section 7 should be less than A in the operating frequency band.

In order to complete the transition piece according to the invention the section 2 is followed by a section 4, which is disposed between the connecting plane between the oval waveguide 5 and the section 2 with the conically widened cross section. The section 4, as illustrated, also has a length less than k and, like the section 3, has a rectangular inner cross section with the central portions of the larger sides X being widened by a circularly cylindrical portion 8. The diameter of the cylindrical portion 8 may be equal to but is preferably less than the largest diameter of the conical portion 6.

The dimensions of the rectangular cross section of the transition piece correspond to the dimensions of the standard rectangular waveguide which is to be connected thereto.

In order to provide an actual example of a transition piece according to the invention and to illustrate the advantages thereof, it will be assumed that thestandard rectangular waveguide to be connected is of IEC-type R84 (larger dimension 28.5 mm and smaller dimension 12.6 mm) and the waveguide 5 with the oval cross section which is to be connected is a smooth aluminum waveguide for the frequency range from 7,700 MHz to 8,600 MHZ. This oval waveguide has a larger axis of 37 mm and smaller axis of 19.5 mm.

When used with the two types of waveguides mentioned above, section 2 with the conically widened portion 6 has a length of 37mm and thus has a length of between 0.69 and 0.824 waveguide wavelengths in the operating frequency band of between 7.7 and 8.6 GHz. The sections 3 and 4 whose rectangular cross sections are widened in the center of the longer sides X by circularly cylindrical sections 7 or 8, respectively, each have a length of 2mm, i.e. have a length of between 0.038 and 0.045 waveguide wavelengths in the operating frequency band. While the greatest diameter of the conically widened portion is 21.5mm, the diameter of the circularly cylindrically widened portion 7 in section 3 is. 16.4mm and that of portion 8 in section 4 is 17.3mm.

The influence of these widened cross sections in line sections, 2, 3, and 4 becomes evident from the loci shown in FIG. 2. All loci are plotted as conductance values in the connecting plane between the waveguide transition piece and the oval waveguide 5. Locus I shows the input admittance of the oval waveguide 5 with respect to the admittance of the rectangular waveguide R84. Locus II shows the input admittance of the waveguide transition piece through conical portions in line section 2 transformed to the connecting plane with the oval waveguide. A comparison of the two loci I and II shows that the reflection factor has been reduced by only about 30% by the insertion of the line section 2 with the conically widened portion. However locus II now has such a position that it can be shifted by means of a parallel capacitance applied in the immediate vicinity of the connecting plane to the center of the diagram (locus Illa). This however, would reduce the reflection factor r in the operating frequency band of 7.7 to 8.6 GHZ only to values of less than r= 0.02. By selecting the parallel capacitance, which is formed by the circularly cylindrical widened portion 8 of the rectangular cross section of waveguide section 4 whose diameter in this case is less than the greatest diameter of the adjacent conical widening of the rectangular cross section slightly too large, the locus IIIb is produced. Finally, by replacing a short portion of waveguide section 2 by waveguide section 3 with the circularly cylindrical widened portion 7 with a diameter which is less than that of the adjacent conical sections and thus acts at this point as a parallel capacitance and at a distance of about k from waveguide section 4, there results locus IV of FIG. 2 for the input admittance of the waveguide transition piece to which the oval waveguide 5 is connected. It can be seen that in this manner a broadbanded matching of the oval waveguide with the rectangular waveguide R84 has been realized in this embodiment with reflection factors in the operating frequency band of less than r 0.0004.

FIG. 3 shows the configuration of a further embodiment of a waveguide transition piece according to the present invention. The waveguide transition piece in this embodiment like the embodiment of FIG. 1 has a generally rectangular inner cross section but has two sections with different cross sections within the linearly conically widened portion 9 formed in the central portion of the longer sides of the rectangular inner cross section. Section 10 here constitutes a circularly cylindrical widened portion whose diameter is greater than that of the adjacent portion of conical portion 9. Section 10 thus forms a parallel capacitance. Section 11, however, has a diameter in its circularly cylindrical widening which is less than that of the adjacent portions of the conical portion 9, and results in a parallel inductance which is for many cases useful. Section 12 which immediately follows the conical portion 9, however, forrns a circularly cylindrically widened portion whose diameter is the same as that of the conical portion at the common connecting plane. The function of section 12 is to transform the impedance. A further waveguide section 13 with a circularly cylindrical deviation from the conical cross section extends from section 12 to the flanging plane with the oval waveguide. The diameter of section 13 is selected to be less than the diameter of the preceding section 12. The function of section 13 is that of a parallel capacitance.

With the structure according to the present invention it is possible to avoid the above-mentioned drawbacks resulting from the use of screwin plugs or soldered plugs, because the widening of the interior of the rectangular waveguide by means of conical portions and the widening by means of circularly cylindrical portions can be produced by turning in the same processing step. In addition to this savings in costs the realizable matching between the waveguides with rectangular and oval cross sections which are to be connected together is substantially improved over the prior art solutions.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are in tended to be comprehended within the meaning and range of equivalents of the appended claims.

We claim:

1. In a waveguide transition piece for the broadbanded, low reflection connection of a standard waveguide having a rectangular inner cross section with a smooth or corrugated waveguide having an oval inner cross section, said transition piece being a waveguide with a substantially rectangular inner cross section with the central portion of the longer sides of said inner cross section of a section of said transition piece having a widened portion which extends, in the form of linearly widened conical sections over a length of no more than 0.85 waveguide wavelengths (A in the direction toward the end of the transition piece to which the oval waveguide is to be connected, said widened portion serving substantially to effect a broadbanded matching of the characteristic impedance of the two waveguides having different inner cross sections which are to be connected by means of concentrated adapter elements which act, at the point where they are disposed, predominantly as parallel capacitances or parallel inductances; the improvement wherein said transition piece includes a further waveguide section disposed between the connecting plane with the oval waveguide and the end of the waveguide section having the conically widened portion, said further waveguide section being no longer than A and having a rectangular inner cross section whose longer sides are uniformly circularly widened in the central portion thereof with the diameter of these widened portions being less than the greatest diameter of said conically widened portion.

2. A waveguide transition piece: as defined in claim 1 further comprising at least one additional waveguide section which is no more than A, in length inserted in the waveguide section with the conically widened portion, said additional waveguide section having a rectangular inner cross section with the central portion of the longer sides being uniformly circularly widened.

3. A waveguide transition piece as defined in claim 2 wherein the diameter of the circularly widened cross section of said additional waveguide sections is different from the diameters of the adjacent conical portions.

4. A waveguide transition piece as defined in claim 2 wherein the diameter of said circularly widened portion of said additional waveguide section is equal to the greatest diameter of the adjacent conical portion. 

1. In a waveguide transition piece for the broad-banded, low reflection connection of a standard waveguide having a rectangular inner cross section with a smooth or corrugated waveguide having an oval inner cross section, said transition piece being a waveguide with a substantially rectangular inner cross section with the central portion of the longer sides of said inner cross section of a section of said transition piece having a widened portion which extends, in the form of linearly widened conical sections over a length of no more than 0.85 waveguide wavelengths ( lambda H), in the direction toward the end of the transition piece to which the oval waveguide is to be connected, said widened portion serving substantially to effect a broadbanded matching of the characteristic impedance of the two waveguides having different inner cross sections which are to be connected by means of concentrated adapter elements which act, at the point where they are disposed, predominantly as parallel capacitances or parallel inductances; the improvement wherein said transition piece includes a further waveguide section disposed between the connecting plane with the oval waveguide and the end of the waveguide section having the conically widened portion, said further waveguide section being no longer than lambda H/8 and having a rectangular inner cross section whose longer sides are uniformly circularly widened in the central portion thereof with the diameter of these widened portions being less than the greatest diameter of said conically widened portion.
 2. A waveguide transition piece as defined in claim 1 further comprising at least one additional waveguide section which is no more than lambda H/8 in length inserted in the waveguide section with the conically widened portion, said additional waveguide section having a rectangular inner cross section with the central portion of the longer sides being uniformly circularly widened.
 3. A waveguide transition piece as defined in claim 2 wherein the diameter of the circularly widened cross section of said additional waveguide sections is different from the diameters of the adjacent conical portions.
 4. A waveguide transition piece as defined in claim 2 wherein the diameter of said circularly widened portion of said additional waveguide section is equal to the greatest diameter of the adjacent conical portion. 